Teachers belonging to the Irish National Teachers Organisation (INTO) have staged a half-day strike in a dispute over pay.
The union's northern secretary Gerry Murphy said its 7,000 members were "fed up and angry".
He led a rally in Space One at Queen's University's Students' Union on Wednesday morning, while members picketed schools.
Mr Murphy, said their strike showed the strength of feeling among teachers about pay.
"Teachers are loath to take strike action, but, having exhausted all the avenues of negotiation available to them, teachers have no options left other than to withdraw their labour."